We discovered in 2002 that the tetramerization (tet) domain of the tumor suppressor p53 can be converted from its native conformation to an alternative conformation with the characteristics of amyloid fibrils. Further, we observed that a cancer-associated mutant form of this domain, with Arg 337 mutated to His, exhibits a significantly heightened propensity to form fibrils compared to the wild-type domain, p53 is a structurally modular protein, and folding of the tet domain is required for tumor suppression. Previously, we showed that the R337H mutation destabilizes the tet domain in a pH-dependent manner and developed a molecular explanation for the tissue specificity of cancer associated with this mutation (adrenal cortical carcinoma (ACC) in children). We feel that there is a link between fibril formation and mutant p53 tumor biology. Consistent with findings for other cancer-associated mutant forms of p53, p53 with the R337H mutation (p53-R337H) accumulates at high levels in the nuclei of ACC tumor cells. Based on our findings for the mutant tet domain, we hypothesize that these nuclear accumulations have fibrilar structure. Further, we suggest that (some) other mutant forms of p53 accumulate in fibrilar structures. We seek to test these hypotheses through structural studies of multi-domain forms of wild-type and mutant p53. A variety of biophysical, biochemical and cell biology methods will be applied to study p53 molecules in vitro, in tumor cells, and in cultured cells derived from tumors. Our aims are: 1) To determine whether wild-type and mutant p53 convert from the native state to amyloid fibrils in vitro, and 2) To determine whether aggregated forms of wild-type and mutant p53 in tumor cells exist in a fibrilar state. P53 is a multifunctional protein that is regulated at many levels, including transcription, post-translational modification and cellular localization. To understand tumorigenesis associated with mutations to p53, we must understand how these different regulatory processes are affected by mutations. While high-resolution structures and extensive biophysical data are available for several domains, the structural and biophysical properties of full-length p53 remain largely a mystery. Demonstrating that mutant p53 molecules exist as fibrils would explain the high stability reported for p53 accumulations and their nuclear localization, would provide a molecular explanation for loss of function, and would offer insights into the development of novel p53-directed therapeutics. [unreadable] [unreadable]